1H-MR spectroscopy at 7.0 T and intra-individual comparison to 3.0 T and 1.5 T

Purpose: To investigate characteristic spectral parameters and quality features of in-vivo 1 H-MRS at 7.0 T and to measure metabolite concentrations in an intra-individual comparison to results obtained at 3.0 T and 1.5 T. Methods: Single-voxel proton MR spectra of parietal white matter were obtained at an ultra-highfield whole body MR unit operating at 7.0 T (Achieva 7.0T, Philips Medical Systems) and at clinical whole body 3.0 T and 1.5 T MR systems (Achieva 3.0T and Intera 1.5T, Philips Medical Systems). Transmit/receive quadrature head coils were used at all field strengths, and the same 3 healthy volunteers were investigated at 7.0 T, 3.0 T, and 1.5 T. PRESS-localized spectra were acquired with TR/TE 2000/47ms and water suppression by dual inversion prepulses, and VOI size (4–8cm 3 ) and localization were held identical at the three field strengths in each volunteer. Absolute concentrations were determined by reference to the internal water signal in unsuppressed 1 H spectra. Postprocessing was performed by time-domain quantification using the MRUI software package. Intra-individual comparison of spectral resolution, SNR, metabolite ratios and absolute concentrations was made at all field strengths. Results: Although magnetic field homogeneity was improved by higher order B0 shimming at 7.0 T and 3.0 T, absolute spectral linewidths (LW) increased at higher field strength due to susceptibility broadening. Nevertheless, taking into account the more than doubled chemical shift dispersion, a net increase in relative line separation Δν/LW (and thus in spectral resolution) of about 40% was achieved at 7.0 T in comparison to 3.0 T. Line broadening also caused that SNR was only about 20% higher at 7.0 T in relation to 3.0 T when calculated from peak amplitudes. However, when considering spectral line integrals, the increase at 7.0 T was close to the predicted linear field dependence. Measurements of metabolite ratios and concentrations at the 3 different field strengths yielded consistent results for choline and creatine with intra-individual variations